1. Field of the Invention
This invention generally relates to shotshells and more particularly to a top wad moisture seal for a shotshell having a roll crimp end closure.
2. Description of the Related Art
A roll crimp end closure for a shotshell typically involves placing a paper, plastic, or metal disk over the load of shot in the shotshell and then rolling the end of the shotshell tube down onto the disk.
An example of this type of end closure is disclosed in U. S. Pat. No. 2,818,810 to Reynolds. The closure disk described in this patent is a circular disk having an approximately semi-circular, axially extending peripheral flange. Upon muzzle exit, this flange causes the closure disk to separate away from the shot so as not to impede the trajectory of the shot column.
Another type of end closure is described in U.S. Pat. No. 3,205,819 to Barrick. This patent discloses an over shot wad which has as a circumferential groove formed in a perimeter edge thereof defining a pair of pliable lips. This wad eliminates the necessity for a roll crimp to retain the wad on top of the shot. The lips are elastically compressed against the inside wall of the tube to secure the wad in place against the shot thus closing the end of the shotshell. The over shot wad is relatively thick in order to support the two lips and is therefore a substantial parasitic mass. In addition, it has a flat disk shape which can impede the down range trajectory of the shot column upon leaving the gun muzzle.
U.S. Pat. No. 3,352,239 to Schinnerer et al discloses a over shot wad for a roll crimp shotshell that has a flat circular disk portion with a peripheral tubular portion. The plastic wad is placed inside the case over the load of shot and the case roll crimped over the tubular portion to hold the wad in place. The wad may have a central portion of reduced and raised thickness to constitute tactile markings to indicate such things as the buck shot size.
U.S. Pat. No. 3,596,600 discloses a plastic shotshell with a plastic disk over shot wad which has a dome shape and resiliently snaps over center into place in an appropriately sized groove molded into the inside wall at the end of the shotshell casing. The disk in this case is snapped over center from a convex outward configuration to a concave outward configuration to snap fit the disk in place.
U.S. Pat. No. 3,673,965 to Herter discloses an over shot wad having a generally disk shape with a thickened rim portion and thickened central hub portion. In addition, radial spokes from the hub to the rim provide addition stiffness to the top wad. The mouth of the shotshell is bent inward to form a resilient bead or lip retainer to retain the top wad in place. This shot wad is made of a soft unbreakable polyethylene material which stays in one piece. Reliance is made on wind catching the radial ribs as pressure veins to clear the over shot wad from the path of the shot charge.
None of these patents discloses a moisture resistant over shot top wad which precludes moisture intrusion during normal field handling of the shotshell. A novel approach to sealing shotshells is disclosed in U.S. Pat. No. 4,991,512 issued to Van Wyk and assigned to the assignee of the present invention. The moisture seal disclosed in this patent is a composite disk of a thermally conductive layer and a thermoplastic layer such as high density polyethylene laminated together. The rim portion of the high density polyethylene layer is bonded or fused to the tubular casing to render the casing impervious to moisture. This moisture seal is very thin and light weight and thus is not preferably designed to be the only end closure member. The seal described in this patent is designed to be positioned over or under the normal end closure such as a star folded or roll crimp.
The deleterious effects of water intrusion into a shotshell can be quite serious. If water seeps into the shot load and is trapped inside for a period of time, it will rust the steel shot and may fuse the shot together into a single mass. In addition, if water gets into the propellant, a "squib" may be produced which could conceivably destroy the gun upon firing of a subsequent round.
Accordingly, there is still a need for a moisture resistant shotshell top wad which can be readily inserted without regard to orientation, provides a good moisture seal, is adapted for use with standard roll crimp tooling, and which has minimal effect on the shot pattern.